Senior South Korean and U.S. diplomats began a new round of negotiations here Thursday on Seoul's pursuit of expanding its peaceful nuclear technology.

The two-day meeting, the third of its kind, will focus on fine-tuning the wording of a draft agreement presented in the previous round, according to officials.

The existing treaty, signed in 1974, expires in March 2014.

South Korea is seeking to revise it to meet its enhanced status as a nuclear energy developer.

Under the pact, South Korea is prohibited from reprocessing its more than 10,000 tons of nuclear waste from some two dozen reactors.

South Korea has proposed "pyroprocessing," a new technique not yet commercialized, to recycle spent fuel, South Korean officials say.

After the second round of talks in March, South Korea and the U.S. launched a committee for a joint study of the characteristics of pyroprocessing.

"There is no political or diplomatic problem," a South Korean official said. "It is purely a technical issue."

Several more rounds of negotiations will be needed to reach an agreement, he added, although South Korea wants to complete the process by next year in consideration of the time necessary for parliamentary ratification.

Campaigning for a nuclear-free world, the U.S. is cautious, however, and U.S. experts expect tough talks.

"The United States will find it difficult to consent to any kind of reprocessing on the Korean Peninsula, particularly if Washington perceives that such a decision would jeopardize the satisfactory resolution of the nuclear issue in North Korea, including a nuclear-weapons-free Korean Peninsula," former State Department official Fred McGoldrick said in a report. He has long experience in nuclear nonproliferation and international nuclear policy at the U.S. Department of Energy and Department of State, where he negotiated civilian nuclear cooperation agreements.

In the talks, South Korea is represented by Park Ro-byug, former ambassador to Ukraine. His U.S. counterpart is Robert Einhorn, the State Department's special adviser for nonproliferation and arms control. (Yonhap News)